1. Field of the Invention
The present invention relates to a discharge lamp to be used as a light source for a projector or the like and, more particularly, to a discharge lamp suitable for a high wattage light source.
2. Description of the Prior Art
Discharge lamps are widely used as light sources for various lighting apparatuses and, in recent years, also used as light sources for image projectors.
To increase the brightness of the projectors, an attempt has rapidly been made to produce a higher-pressure and higher-wattage discharge lamp. However, an increase in the inside pressure of the discharge lamp entails a high risk of explosion of the discharge lamp, because a gas filled in the discharge lamp expands due to a temperature rise of the discharge lamp when the discharge lamp is lit.
FIG. 21 is a vertical sectional view of a conventional discharge lamp, in which reference numerals 1 and 2 denote a lamp body and a reflector (reflection mirror), respectively.
A thick front glass 3 is fitted on a front portion of the reflector 2 so that, even if the lamp body 1 explodes, broken pieces thereof are prevented from scattering forwardly of the discharge lamp. That is, the lamp body 1 is hermetically enclosed by the reflector 2 and the front glass 3.
With the hermetically enclosed structure, however, air around the lamp body 1 is heated when the lamp body 1 is lit, so that the temperature in a hermetic space defined by the reflector 2 and the front glass 3 is significantly increased. In consideration of such thermal conditions, the upper limit of the wattage of the lamp body 1 is 150 W in practice and, therefore, it has been difficult to further increase the inside pressure and wattage of the lamp body.
It is therefore an object of the present invention to provide a discharge lamp which employs a higher-pressure and higher-wattage lamp body and is capable of effectively preventing the scattering of broken pieces of the lamp body at explosion of the lamp body.
In accordance with a first aspect of the present invention, there is provided a discharge lamp which comprises a lamp body, a reflector, and a front glass fitted on a front portion of the reflector, wherein the reflector has two vent holes in which mesh sheets or perforated plates are fitted. (FIGS. 1-4)
With this arrangement, air heated in an inside space of the reflector can be released from the discharge lamp through mesh of the mesh sheets or perforations of the perforated plates, so that an excessive temperature rise around the lamp body can be prevented. Therefore, a higher-pressure and higher-wattage lamp body having a wattage higher than 150 W can be employed as the lamp body to be housed in the inside space of the reflector of the discharge lamp.
In accordance with a second aspect of the present invention, there is provided a discharge lamp which comprises a lamp body, a reflector, and a front glass fitted on a front portion of the reflector, wherein the reflector has two vent holes in which plates formed with slits are fitted, wherein the plates have baffles provided along the slits for directing outside air introduced into an inside space of the reflector through the slits toward a high temperature portion of the lamp body. (FIGS. 5,6)
With this arrangement, outside air introduced into the inside space through the slits are allowed to uniformly flow toward the lamp body by the baffles to efficiently cool the ambience of the lamp body, and then released to the outside through another slits.
Thus, the ambient temperature of the lamp body is prevented from being excessively increased. Therefore, a higher-pressure and higher-wattage lamp body having a wattage higher than 150W can be employed as the lamp body of the discharge lamp.
In the discharge lamp according to the first or second aspect of the invention, the vent holes may be a through-hole formed in the reflector (FIGS. 7,8) or a cut-away portion formed in the reflector in association with the front portion thereof. (FIGS. 1-6)
With this arrangement, the reflector is effectively provided with the vent holes in which the mesh sheets or the perforated plates are fitted.
In accordance with a third aspect of the present invention, there is provided a discharge lamp which comprises a lamp body, a reflector, and a front glass fitted on a front portion of the reflector, wherein the reflector has two vent portions 51 having a multiplicity of through-holes 5a formed therein (FIGS. 9,10), or shaped like the teeth of a comb (FIGS. 11,12).
With this arrangement, the reflector itself functions as a perforated plate for ventilation without the use of the mesh sheet or the perforated plate.
In accordance with a fourth aspect of the present invention, there is provided a discharge lamp which comprises a lamp body, a reflector having the lamp body at the center of it, a ring spacer fitted on a front portion of the reflector, and a front glass fitted on a front portion of the ring spacer, wherein the ring spacer has vent holes having mesh of the mesh sheets, perforated plates or plates formed with a slit, wherein the plates have baffles provided along the slits for directing outside air introduced into an inside space of the reflector through the slits toward a high temperature portion of the lamp body.
In accordance with the fifth aspect of the present invention (FIGS. 19,20), the ring spacer has vent portions 51 having a multiplicity of through-holes formed therein ,or shaped like the teeth of a comb.